1. Field of the Invention
The present invention relates to a technique of a system for handling stud bolt holes, and more particularly to a system for cleaning and inspecting stud bolt holes, and for managing damage histories of the stud bolt holes, which allows an operator to clean stud bolt holes, inspect the stud bolt holes with the naked eye, and manage damage histories of the stud bolt holes, in which the stud bolts holes serve to fix a nuclear reactor, a nuclear reactor coolant pump head, and a pressure vessel main body thereto.
2. Description of the Related Art
In general, referring to FIG. 1, a plurality of holes 30 for coupling a pressure vessel main body by using stud bolts are formed on a main flange 1 which is a nuclear reactor coolant pump head. The number of holes 30 may be preferably implemented by 48, 54 or 58.
Although slightly different in size by types of power plants, the nuclear reactor coolant pump head and the nuclear reactor pressure vessel main body are normally coupled by stud bolts and holes as shown in FIG. 2. Such coupling serves to maintain the airtightness and safety in the nuclear reactor which must be kept at a high temperature and a high pressure during operation.
Since the stud bolts and the holes are coupled to each other by a tensioning process, screw threads of the stud bolts and the holes may be easily damaged. Therefore, the cleaning states of the stud bolts and the holes have considerable influence on coupling intensity and damages thereof. The cleaning states of the stud bolts and the holes also prevent adherence of the stud bolts and the holes in disassembly. It is thus very important to maintain the stud bolt holes clean.
As illustrated in FIG. 3, the stud bolt holes 30 are cleaned by using an electromotive brush 2. An operator uses the electromotive brush 2 in general wet and dry environments. First, the operator applies cleaning oil to the holes 30, cleans the holes 30 by the brush 2, wraps a cleaning cloth round the brush 2, and wipes the holes 30. The operator accesses the holes 30 and directly performs these operations.
The MHI companies in Japan have suggested a cleaning device for cleaning stud bolt holes in a dry atmosphere by using a brush. However, it is not used due to many operational problems.
The cleaning device cannot clean the stud bolt holes in a wet atmosphere. In addition, the cleaning device does not allow the operator to inspect the holes with the naked eye and manage histories of the holes.
Accordingly, the operator cleans the stud bolt holes in the wet atmosphere by using the electromotive brush or a dustcloth, and inspects the stud bolt holes with the naked eye by using a mirror.
In the conventional method for cleaning the stud bolt holes, the cleaning operation and the naked eye inspection are individually carried out, and the damage histories of the holes are not managed. Also, it is difficult to generate comparative data for comparing states before and after crack generation and systematically manage the histories of the holes.
The operator who cleans the holes may become a victim of radiation. Furthermore, cleaning efficiency is not improved due to manual operations.